Diagnostic circuit for a tweeter ina loudspeaker combination

ABSTRACT

A diagnostic circuit for a treble loudspeaker of a loudspeaker combination of a low-frequency output stage, and a method for diagnosing the functionality of the treble loudspeaker. In order to determine the functionality of the treble loudspeaker with relatively little complexity and high reliability, a diagnostic circuit is provided that comprises an HF signal-generating device for outputting an HF voltage signal, at least one terminal for a loudspeaker combination, a measuring resistor that, upon connection of the loudspeaker combination to the terminal, forms therewith a voltage divider circuit, and a measurement device for measuring a complex measured voltage dropping in the voltage divider circuit and for ascertaining a condition of the treble loudspeaker of the loudspeaker combination.

FIELD OF THE INVENTION

The present invention relates to a diagnostic circuit for a trebleloudspeaker of a loudspeaker combination, as well as a method fortesting a treble loudspeaker of a loudspeaker combination.

BACKGROUND INFORMATION

In low-frequency output stages of loudspeaker systems that are provided,for example, in a motor vehicle, a bass and a midtone loudspeaker, or amidtone/bass loudspeaker, are generally connected directly to theamplifiers of the low-frequency output stages, and a treble loudspeakeris coupled capacitatively. The functionality of this loudspeakercombination is tested in particular upon installation into a vehicle,and as applicable at maintenance intervals or in the event ofmalfunctions. Interruptions or short circuits in the supply leads may,in particular, occur in this context. Testing of the bass, midtone, ormidtone/bass loudspeakers can be accomplished directly in resistivefashion using an applied DC voltage. A corresponding testing of thecapacitatively connected treble loudspeaker is, however, not therebypossible. This testing is accordingly usually performed by input of atreble signal and acoustic perception. Such testing is, however,time-consuming and imprecise in the context of automated production.

Also conventional are circuit assemblages in which the currentconsumption of an output stage 1C is measured upon application of a highLF frequency and a high output level. For this purpose, a measurementdevice must be appropriately provided in the power supply to the poweroutput stages.

SUMMARY

A diagnostic circuit and method according to example embodiments of thepresent invention as may have, in contrast, the particular advantagethat an accurate measurement of the functionality of a trebleloudspeaker of a loudspeaker combination is possible with relativelylittle complexity.

According to the present invention, testing of the treble loudspeaker isthus made possible by the fact that a voltage divider circuit isconstituted from a preferably purely ohmic resistor and the loudspeakercombination, and a voltage drop within that voltage divider circuit ismeasured and evaluated. In particular, the voltage drop can be measuredin this context as a complex measured voltage at the loudspeakercombination; in principle, however, a measurement of the voltage drop atthe measuring resistor is also possible.

In the voltage divider circuit, the bass, midtone, or midtone/bassloudspeaker or loudspeakers are connected in parallel with the couplingcapacitor and the treble loudspeaker. The functionality or condition ofthe treble loudspeaker affects the complex total resistance of theloudspeaker combination at the HF frequency. An interruption at thetreble loudspeaker or its supply leads results in an increase in thetotal resistance, and a short circuit correspondingly in a decrease inthe total resistance, as compared with the total resistance when thetreble loudspeaker is functional. Since the loudspeakers designed forlower frequencies have a higher inductance than the treble loudspeaker,they have little influence on the measured signal.

The measured complex measured voltage can be evaluated, for example, bymeasuring the peak value phase-shifted with respect to the outputsignal, or by way of a rectifier circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained below, in connection with severalembodiments, with reference to the figures.

FIG. 1 is a block diagram of a power output stage having a diagnosticcircuit according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a power output stage having a diagnosticcircuit according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

As shown in FIG. 1, a first output amplifier V1 of a low-frequencyoutput stage is connected via a first terminal A1 to the positive poleon loudspeaker combination 4, and a second output amplifier V2 of thelow-frequency output stage is connected via a second terminal A2 to thenegative pole of loudspeaker combination 4. Loudspeaker combination 4has a midtone/bass loudspeaker LS1 that is connected to terminals A1,A2, and a treble loudspeaker LS2 connected via a capacitor C7 inparallel with LS1. For diagnosis of treble loudspeaker LS2, loudspeakersLS1 and LS2 are activated and amplifiers V1, V2 are switched off and arethus high-resistance. A processor 10 outputs an HF input signal s1 thatis outputted via an impedance converter 3 as HF voltage signal s2.Processor 10 thus constitutes, with impedance converter 3, an HFvoltage-generating device 2. HF input signal s1 is transferred through aresistor R2 and a capacitor C4 to first terminal A1, i.e., to thepositive pole of loudspeaker combination 4. Second terminal A2 isgrounded through a connecting device 6. At A1, the voltage drop atloudspeaker combination 4 and at connecting device 6 is picked off by ameasurement device 11 as complex measured voltage UA1.

In HF voltage-generating device 2, HF input signal s1 having a frequencygreater than or equal to 20 KHz, and a diagnostic signal d constitutinga DC voltage signal, are output by processor 10. Diagnostic signal dsets a diagnostic mode. Processor 10 also (in a manner not shown)switches output amplifiers V1, V2 to high resistance by way ofdiagnostic signal d. HF voltage signal s is conveyed through a capacitorC2, together with diagnostic signal d, to an emitter follower transistorV3 of impedance converter 3, the working point of the base of emitterfollower transistor V3 being set by way of resistors R4, R6. A furthertransistor V4 and a resistor R3 constitute a constant-current sourceconnected to the emitter of V3, V4 being made conductive uponapplication of diagnostic signal d to its base. Impedance converter 3outputs an HF voltage signal S2 that drops to ground through measuringresistor R2, capacitor C4, loudspeaker combination 4, and connectingdevice 6.

Connecting device 6 has a transistor V5 that is modulated by diagnosticsignal d and connects an AC voltage present at second terminal A2 toground in low-resistance fashion. With suitable dimensioning ofcapacitors C4, C7, HF voltage signal S2 thus drops substantially at aseries circuit of R2 and the parallel-connected loudspeakers LS1 andLS2.

Measured voltage UA1 present at A1 is received by a measurement device11 that is constituted by a resistor R1, a capacitor C8, and processor10 that serves as the evaluation device. Measured voltage UA1 isphase-shifted with respect to S1, in particular because of theimpedances of LS1 and LS2. In the example embodiment shown in FIG. 1,the phase-shifted peak value is determined by measurement device 11, andbecause R2 is known, the impedance of loudspeaker combination 4 isascertained therefrom. Since LS1 has a high inductance, the voltage dropbetween A1 and A2 is determined substantially by LS2. Measurement device11 thus identifies a low measured voltage (or a measured voltage with alow absolute value) in the event of a short circuit, a high measuredvoltage in the event of an interruption at LS2, and a moderate measuredvoltage when LS2 is in the functional condition.

In the example embodiment shown in FIG. 2, unlike in the first exampleembodiment, a measurement device 12 is used in which a resistor R1,capacitor C7, a Schottky diode D1, and a grounded capacitor C1 serve torectify the received AC voltage signal, so that processor 10 can receivea rectified voltage.

1-17. (canceled)
 18. A diagnostic circuit for a treble loudspeaker of aloudspeaker combination, the diagnostic circuit, comprising: a highfrequency (HF) signal-generating device configured to output an HFvoltage signal; at least one terminal for the loudspeaker combination; ameasuring resistor that, upon connection of the loudspeaker combinationto the terminal, forms therewith a voltage divider circuit; and ameasurement device configured to measure a complex measured voltage dropin the voltage divider circuit and to ascertain a condition of thetreble loudspeaker of the loudspeaker combination.
 19. The diagnosticcircuit as recited in claim 18, wherein the measuring resistor isbetween the HF signal-generating device and the terminal, and themeasurement device measure a measured voltage drop substantially at theloudspeaker combination.
 20. The diagnostic circuit as recited in claim19, further comprising: a capacitor connected between the measuringresistor and the terminal.
 21. The diagnostic circuit as recited inclaim 18, wherein the HF signal-generating device includes an HF signalsource configured to output an HF input signal, and a downstreamimpedance converter that is configured to be switched on by a DC voltagediagnostic signal.
 22. The diagnostic circuit as recited in claim 21,wherein the impedance converter includes an emitter follower transistorthat is configured to receive the HF input signal and the diagnosticsignal.
 23. The diagnostic circuit as recited in claim 22, wherein acurrent source which includes a second transistor configured to beswitched on by the diagnostic signal is an emitter resistor of theemitter follower transistor, a collector of the second transistor isconnected to an emitter of the emitter follower transistor, an emitterof the second transistor is grounded through a resistor, and a base ofthe second transistor is configured to be activated by the diagnosticsignal.
 24. The diagnostic circuit as recited in claim 23, wherein thebase of the second transistor is configured to be activated by the HFinput signal.
 25. The diagnostic circuit as recited in claim 18, whereinthe measurement device is configured to ascertain a peak value of themeasured voltage.
 26. The diagnostic circuit as recited in claim 24,wherein the measurement device includes a resistor connected to theterminal device, a capacitor connected to the resistor, and anevaluation device.
 27. The diagnostic circuit as recited in claim 18,wherein the measurement device includes a rectifier circuit configuredto rectify the measured voltage and output a rectified measured voltagesignal to an evaluation device.
 28. The diagnostic circuit as recited inclaim 26, wherein the rectifier circuit includes a series circuitincluding a resistor, a capacitor, and a Schottky diode, the seriescircuit being grounded through a second capacitor.
 29. The diagnosticcircuit as recited in claim 18, wherein the measurement device isconfigured to deduce a short circuit of the treble loudspeaker when alow measured voltage is ascertained, a correct condition of the trebleloudspeaker from a moderate measured voltage, and an interruption at thetreble loudspeaker from a high measured voltage.
 30. The diagnosticcircuit as recited in claim 18, wherein the measuring resistor is apurely ohmic resistor.
 31. A method for testing a treble loudspeaker ofa loudspeaker combination, comprising: outputting a high frequency (HF)voltage signal to a voltage divider circuit made up of a measuringresistor and the loudspeaker combination; measuring a complex measuredvoltage drop in the voltage divider; and deducing a condition of thetreble loudspeaker from the measured voltage.
 32. The method as recitedin claim 31, wherein the measured voltage is measured as a voltage dropat the loudspeaker combination.
 33. The method as recited in claim 31,wherein a short circuit at the treble loudspeaker is deduced when a lowmeasured voltage is ascertained at the loudspeaker combination, acorrect condition of the treble loudspeaker is deduced when a moderatemeasured voltage is ascertained at the loudspeaker combination, and aninterruption at the treble loudspeaker is deduced when a high measuredvoltage is ascertained at the loudspeaker combination.
 34. The method asrecited in claim 30, wherein a peak value of the complex measuredvoltage is measured and subsequently evaluated.
 35. The method asrecited in claim 31, wherein the complex measured voltage is rectifiedand subsequently evaluated.